Refuse PUSH_PROMISE while unacked local ENABLE_PUSH is 0

After we sent SETTINGS including ENABLE_PUSH = 0, peer may already
issue PUSH_PROMISE before receiving our SETTINGS and react it to
SETTINGS ACK.  Previously we accept this PUSH_PROMISE.  In this
commit, we check the pending ENABLE_PUSH value and if it means
disabling push, we refuse PUSH_PROMISE with RST_STREAM of error
REFUSED_STREAM.

lib/nghttp2_session.c

@@ -383,6 +383,7 @@ static int session_new(nghttp2_session **session_ptr,
 
   (*session_ptr)->pending_local_max_concurrent_stream =
       NGHTTP2_INITIAL_MAX_CONCURRENT_STREAMS;
+  (*session_ptr)->pending_enable_push = 1;
 
   if (server) {
     (*session_ptr)->server = 1;
@@ -3901,6 +3902,7 @@ int nghttp2_session_update_local_settings(nghttp2_session *session,
 
   session->pending_local_max_concurrent_stream =
       NGHTTP2_INITIAL_MAX_CONCURRENT_STREAMS;
+  session->pending_enable_push = 1;
 
   return 0;
 }
@@ -4129,7 +4131,8 @@ int nghttp2_session_on_push_promise_received(nghttp2_session *session,
   }
   session->last_recv_stream_id = frame->push_promise.promised_stream_id;
   stream = nghttp2_session_get_stream(session, frame->hd.stream_id);
-  if (!stream || stream->state == NGHTTP2_STREAM_CLOSING) {
+  if (!stream || stream->state == NGHTTP2_STREAM_CLOSING ||
+      !session->pending_enable_push) {
     if (!stream) {
       if (session_detect_idle_stream(session, frame->hd.stream_id)) {
         return session_inflate_handle_invalid_connection(
@@ -6105,8 +6108,10 @@ int nghttp2_session_add_settings(nghttp2_session *session, uint8_t flags,
     return rv;
   }
 
-  /* Extract NGHTTP2_SETTINGS_MAX_CONCURRENT_STREAMS here and use
-     it to refuse the incoming streams with RST_STREAM. */
+  /* Extract NGHTTP2_SETTINGS_MAX_CONCURRENT_STREAMS and ENABLE_PUSH
+     here.  We use it to refuse the incoming stream and PUSH_PROMISE
+     with RST_STREAM. */
+
   for (i = niv; i > 0; --i) {
     if (iv[i - 1].settings_id == NGHTTP2_SETTINGS_MAX_CONCURRENT_STREAMS) {
       session->pending_local_max_concurrent_stream = iv[i - 1].value;
@@ -6114,6 +6119,13 @@ int nghttp2_session_add_settings(nghttp2_session *session, uint8_t flags,
     }
   }
 
+  for (i = niv; i > 0; --i) {
+    if (iv[i - 1].settings_id == NGHTTP2_SETTINGS_ENABLE_PUSH) {
+      session->pending_enable_push = iv[i - 1].value;
+      break;
+    }
+  }
+
   return 0;
 }
 

lib/nghttp2_session.h

@@ -253,6 +253,9 @@ struct nghttp2_session {
   /* Unacked local SETTINGS_MAX_CONCURRENT_STREAMS value. We use this
      to refuse the incoming stream if it exceeds this value. */
   uint32_t pending_local_max_concurrent_stream;
+  /* Unacked local ENABLE_PUSH value.  We use this to refuse
+     PUSH_PROMISE before SETTINGS ACK is received. */
+  uint8_t pending_enable_push;
   /* Nonzero if the session is server side. */
   uint8_t server;
   /* Flags indicating GOAWAY is sent and/or recieved. The flags are

tests/nghttp2_session_test.c

@@ -2201,6 +2201,7 @@ void test_nghttp2_session_on_push_promise_received(void) {
   nghttp2_nv *nva;
   size_t nvlen;
   nghttp2_mem *mem;
+  nghttp2_settings_entry iv = {NGHTTP2_SETTINGS_ENABLE_PUSH, 0};
 
   mem = nghttp2_mem_default();
   memset(&callbacks, 0, sizeof(nghttp2_session_callbacks));
@@ -2380,6 +2381,25 @@ void test_nghttp2_session_on_push_promise_received(void) {
 
   nghttp2_frame_push_promise_free(&frame.push_promise, mem);
   nghttp2_session_del(session);
+
+  /* If local_settings.enable_push = 0 is pending, but not acked from
+     peer, incoming PUSH_PROMISE is rejected */
+  nghttp2_session_client_new(&session, &callbacks, &user_data);
+
+  stream = nghttp2_session_open_stream(session, 1, NGHTTP2_STREAM_FLAG_NONE,
+                                       &pri_spec_default,
+                                       NGHTTP2_STREAM_OPENING, NULL);
+  /* Submit settings with ENABLE_PUSH = 0 (thus disabling push) */
+  nghttp2_submit_settings(session, NGHTTP2_FLAG_NONE, &iv, 1);
+
+  nghttp2_frame_push_promise_init(&frame.push_promise, NGHTTP2_FLAG_END_HEADERS,
+                                  1, 2, NULL, 0);
+
+  CU_ASSERT(NGHTTP2_ERR_IGN_HEADER_BLOCK ==
+            nghttp2_session_on_push_promise_received(session, &frame));
+
+  nghttp2_frame_push_promise_free(&frame.push_promise, mem);
+  nghttp2_session_del(session);
 }
 
 void test_nghttp2_session_on_ping_received(void) {